1. Field of the Invention
This invention relates to conjugated fatty acid containing monoglycerides and a process for preparing them. More particularly, this invention relates to conjugated fatted acid containing monoglycerides which are useful for such purposes as an emulsifier of foods and an additive for beverages, and to a process for preparing the conjugated fatted acid containing monoglycerides by the esterification reaction of conjugated fatty acid containing free fatty acid and glycerol as the substrates in the presence of lipase or by the continuous reaction of esterification and glycerolysis in the same reaction system.
2. Background Art
Conjugated linoleic acid has a variety of physiological activities such as anticarcinogenic, body fat reducing, antiarteriosclerotic and antiallergic effects, and used as a healthy food in the form of a free fatty acid but not in the form of a monoglyceride. Conventional fatty acid glycerol esters of non-conjugated fatty acids have been used as emulsifiers in various fields of foods, pharmaceuticals and cosmetics, and among them monoglycerides are most conveniently used. Conventional monoglycerides of non-conjugated fatty acids are industrially produced by chemical alcoholysis of oils and fats with two molar equivalents of glycerol in the presence or in the absence of metal catalysts at high temperatures and high pressures.
However, the conventional chemical methods cannot be applied to the preparation of conjugated fatty acid containing monoglycerides which contain unstable conjugated linoleic acid, and in this context no reports concerning conjugated fatty acid containing monoglycerides and the method of preparing them have been made as long as the present inventors are aware.
In addition, the methods for synthesizing monoglycerides of non-conjugated long chain fatty acids utilizing an enzyme reaction are disclosed for example in Japanese Patent Laid-Open Publication No. 268299/1997 and Japanese Patent Publication No. 12112/1992. The former publication proposes the method for synthesizing efficiently a monoglyceride by glycerolysis of a triglyceride in the presence of a lipase derived from genus Pseudomonas. However, when a conjugated fatty acid monoglyceride is intended to be prepared by the method, the monoglyceride can be prepared only after the conjugated fatty acid, which is usually available in the form of a free fatty acid, is first converted into a triglyceride. In addition, the latter publication proposes the method for preparing a monoglyceride by esterifying a free fatty acid and a glyceride in the presence of mono- and di-glyceride lipase. In this method, the reaction is carried out at 30° C., so that the monoglyceride content in the total glycerides reaches 90% or more when the esterification degree is 60% or less, while a diglyceride as a by-product is observed and the contents of the monoglyceride and the diglyceride become substantially equivalent when the esterification degree is increased to a level of 90% or more.
Conjugated fatty acids possess a variety of physiological activities and employed as healthy foods in the free fatty acids as described above. The conjugated fatty acids are expected to be supplied in the form of monoglycerides for developing the uses as the additives or emulsifiers to a variety of foods, particularly drinks. However, because of the thermal-unstableness of the conjugated fatty acids as described above, the chemical method which has been conventionally used for the preparation of non-conjugated fatty acid glycerides cannot be applied to the preparation of the conjugated fatty acid glycerides, and the enzymatic methods which have hitherto been proposed for the preparation of non-conjugated fatty acid glycerides can be applied effectively only to the glycerolysis which uses a lipase derived from a specific microorganism (genus Pseudomonas) as a catalyst (Japanese Patent Laid-Open Publication No. 268299/1997; J. Am. Oil Chem. Soc., 68, 6–10, 1991) and to the esterification reaction in which the esterification degree is maintained at a low level (Japanese Patent Publication No. 12112/1992).